1. The Field of the Invention
This invention relates to valve apparatus and, more specifically, to a novel servovalve apparatus for use in fluid systems to selectively direct or "port" fluid flow.
2. The Background Art
Fluid systems are frequently used in mechanical devices as a means of controlling or positioning various mechanical components. As used herein, the term "fluid" is used generally to refer to any substance which is capable of flowing under pressure through a conduit. Thus, the term "fluid" encompasses both gasses and liquids, and the general term "fluid systems" is intended to include both pneumatic and hydraulic systems.
A fluid system typically comprises a pump for pressurizing the fluid which is then used to provide the force necessary to position and/or control a desired mechanical component. For example hydraulic systems are often used to control shovels or scoops on heavy construction machinery. Similarly, pneumatic systems are frequently employed in the field of robotics to control the position and movement of a desired object, such as, for example, a robotic arm.
Appropriate fluid controlling valves are essential for the proper operation of virtually all fluid systems. For example, a valve may be used to direct pressurized fluid first to one side and then the other of a plunger which is slidable positioned within an elongated housing. The operation of the valve thus controls the flow of pressurized fluid to each side of the plunger and thereby the position of the plunger within the housing.
Examples of some of the more commonly used valves in fluid systems are poppet valves (which control fluid flow by a "pinching" action) and spool valves (which control fluid flow by selective alignment of fluid channels in a spool with orifices in a sleeve in which the spool is slidable disposed). Poppet valves are generally not well suited for servovalve applications, typically have a significant lag time in their operation, and many times have leakage problems. Spool valves require very tight tolerances to avoid leakage between the spool and sleeve thus making them expensive to manufacture and maintain. Also, because of the tight tolerances, significant frictional forces can be generated causing wear in the valves.
A valve having somewhat more recent origin is the jet pipe valve, often called a flow-dividing valve. A jet pipe valve comprises a fluid pipe having a small orifice on its downstream end. Fluid flows through the pipe at a substantially constant rate, and the small orifice produces a "jet" of fluid out of the end of the pipe. The pipe is provided with a suitable actuator device which selectively directs the fluid jet toward one or more nearby fluid paths. By appropriately positioning the fluid pipe, the ratio of fluid flowing into the nearby fluid paths can be controlled.
Conventional jet pipe valves suffer from significant fluid leakage and are quite inefficient in their use of fluid power. The operation of jet pipe valves is also somewhat unpredictable at high pressures and high fluid flow rates. Consequently, prior art jet pipe valves typically incorporate small orifices (less than 0.005") and operate at fluid flow rates on the order of 0.1 gallons per minute. Conventional jet pipe valves are also typically quite bulky. Due to the significant tangential forces present in jet pipe valves, bulky mechanical actuators are often used. Torsional springs and other balancing mechanisms are also often employed in jet pipe valves in an effort to improve valve operation. Consequently, prior art jet pipe valves are often very difficult to properly maintain and adjust during use.